In the process for forming a high contrast image by development of silver halide photographic elements necessary to produce useful images for graphic arts processes, special developers known in the art as "lith" developers are used. The high contrast is achieved by using the infectious development as described in Journal of the Franklin Institute, vol. 239, 221-230 (1945). These developers exhibit an induction period prior to the development of exposed silver halides, after which the infections development occurs, thus giving rise to high contrast.
The typical "lith" developers contains only a single developing agent of the dihydroxybenzene type, such as hydroquinone. In order to enhance the infectious development, "lith" developers contain an unusually low content of alkali sulfite. This sulfite content renders the developer more prone to aerial oxidation, especially when used in combination with processing machines and, more particularly, with rapid access processing machines, where the developer degradation is accelerated.
Moreover, the delay in the start of development caused by the long induction period of hydroquinone developers lengthens the processing time and delays access to the finished product. While the induction period has been eliminated and processing time has been reduced by the use of the so-called "rapic access" developers containing both hydroquinone and a superadditive developing agent such as phenidone or metol, these rapid access developers are not useful for lithographic purposes because they cannot produce the necessary high contrast. This is because rapic access developers have a high sulfite content which prevents infectious development and cause lower contrast than "lith" developers.
Processes for obtaining high contrast development of silver halide photographic emulsions have been disclosed by adding a hydrazine compound to the silver halide emulsion and developing the emulsion with a developer having a pH as high as 12.8. The use of hydrazine compounds allows the use of auxiliary developing agents in combination with the dihydroxybenzene developing agent in order to increase its development capacity. It also allows the use of relatively high sulfite concentrations to protect the developing agents against oxidation, thereby increasing the developer stability. However, the high pH level necessary to get the high contrast from the use of the hydrazine compound makes the relative life of the developing solution relatively short.
It is desirable to combine the high contrast of "lith" developers with the stability and processing speed of the rapid access developers, as described in U.S. Pat. No. 4,269,929. Reference can also be made to Japanese patent application Ser. No. J6 0093-433.